Low noise, high repetition rate mode-locked lasers have a number of potential applications in signal processing and coherent communications as described in P. J. Delfyett, S. Gee, M. T. Choi, H. Izadpanah, W. Lee, S. Ozharar, F. Quinlan, T. Yimaz, “Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications,” J. Lightwave Technol., vol. 7, pp. 2701-2719, 2006. For applications such as the generation of arbitrary RF waveforms and photonic sampling, pulse-to-pulse timing and amplitude jitter are more important than optical frequency stability, and laser cavities can be designed that sacrifice optical stability in favor of increased timing stability as described in S. Gee, S. Ozharar, F. Quinlan, J. J. Plant, P. W. Juodawlkis, P. J. Delfyett, “Self stabilization of an actively mode-locked semiconductor-based fiber-ring laser for ultralow jitter,” Photon. Technol. Lett., vol. 19. pp. 498-500. However, a number of applications such as optical code division multiple access (OCDMA) and optical arbitrary waveform synthesis require a set of phase locked frequencies with multigigahertz spacing and high stability.
A successful method to simultaneously achieve low timing and amplitude jitter as well as optical frequency stability is using an intracavity etalon in a harmonically mode-locked laser as described in F. Quinlan, S. Gee, S. Ozharar, P. J. Delfyett, “Frequency stabilized low timing jitter mode-locked laser with an intracavity etalon,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies 2007 Technical Digest (Optical Society of America, Washington, D.C., 2007), CThHH6. Harmonic mode-locking can be described in the frequency domain as a collection of interleaved optical supermodes. Each optical supermode consists of phase locked modes separated by the pulse repetition rate whereas different supermodes are separated by the inverse of the cavity round trip time as described in T. Yilmaz, C. M. Depriest, A. Braun, J. Abeles, P. J. Delfyett, “Noise in fundamental and harmonic modelocked semiconductor lasers: experiments and simulations,” J. Quantum Electron., vol. 39, pp. 838-849, 2003.
Placing a high finesse etalon into the laser cavity with a free spectral range equal to the pulse repetition rate selects a single optical supermode that can then be used for frequency domain applications. Moreover, the optical frequencies can be stabilized via the Pound-Drever-Hall laser frequency stabilization method using the same intracavity etalon as described in F. Quinlan, supra, and in R. W. Dreyer, P. J. L. Hall, F. V. Kowalski, J. Hough, G. M. Ford, A. J. Munley, H. Ward, “Laser phase and frequency stabilization using an optical resonator,” Appl. Phys. B. vol. 31, pp. 97-105, 1983. By selecting a single optical supermode, the intracavity etalon also suppresses the supermode noise spurs that contribute to the pulse-to-pulse timing and amplitude noise. Also, by using a long laser cavity and harmonic mode-locking, the linewidth of the individual optical modes can be reduced while a high pulse repetition rate is maintained. The narrow optical linewidths produced are advantageous for high spectral efficiency coherent communication modulation formats as described in J. M. Kahn, “Modulation and Detection Techniques for Optical Communication Systems,” in Optical Amplifiers and Their Applications and Coherent Optical Technologies and Applications on CD-ROM (The Optical Society of America, Washington, D.C., 2006), CThC1, and the reduction of the spontaneous emission contribution to the timing jitter as described in T. Yilmaz, supra.
In addition to spontaneous emission, a major source of timing jitter in an actively mode-locked laser is the phase noise of the RF source used for mode-locking. A way to remove this source of timing jitter is to exploit the high Q of a mode-locked laser and convert it into a coupled optoelectronic oscillator as described in N. Yu, E. Salik, L. Maleki, “Ultralow-noise mode-locked laser with coupled optoelectronic oscillator configuration,” Opt. Lett., vol. 30, pp. 1231-1233, 2005. However, in the conventional coupled optoelectronic oscillator, no effort is made to generate a stabilized optical frequency comb.
To solve the problems encountered with the prior art, combining the technique of incorporating a high finesse etalon in a harmonically mode-locked laser with the conventional coupled optoelectronic oscillator, a completely self contained optical frequency stabilized oscillator was built and characterized. With the incorporation of an etalon, a coupled optoelectronic oscillator can be utilized for a host of new applications relying on a stabilized optical frequency comb.